This article is about scientific theories of the origin of the universe. For mythical explanations, see Creation myth. For the Björk song, see Cosmogony (song).
There is vast consensus among physicists that our universe started with a Big Bang from a state of gravitational singularity. The origins of that singularity remain unclear.
Cosmogony (or cosmogeny) is any scientific theory concerning the coming into existence (or origin) of either the cosmos (or universe), or the so-called "reality" of sentient beings.[1][2] Developing a complete theoretical model has implications in both the philosophy of science and epistemology.
The Big Bang theory is the prevailing cosmological model of the early development of the universe.[3] The most commonly held view is that the universe was once a gravitational singularity, which expanded extremely rapidly from its hot and dense state. While this expansion is well-modeled by the Big Bang theory, the origins of the singularity remains one of the unsolved problems in physics.
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Contents
- 1 Etymology
- 2 Overview
- 3 Cosmogony compared with cosmology
- 4 Epistemological limitations to cosmogony
- 5 Theoretical scenarios
- 5.1 Planck time limitations to cosmogony
- 6 See also
- 7 References
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Etymology
The word comes from the Greek κοσμογονία or κοσμογενία (from κόσμος- "cosmos", "the world") and the root of γί(γ)νομαι / γέγονα ("to be born, come about"). In astronomy, cosmogony refers to the study of the origin of particular astrophysical objects or systems, and is most commonly used in reference to the origin of the solar system.[1][2]
Overview
The Big Bang theory is the prevailing cosmological model of the early development of the universe.[4] The most commonly held view is that the universe was once a gravitational singularity, which expanded extremely rapidly from its hot and dense state. While this expansion is well-modeled by the Big Bang theory, the origins of the singularity remains one of the unsolved problems in physics.
Projection of a Calabi-Yau manifold from string theory. In quantum physics, there remain different, plausible theories regarding what combination of "stuff", space, or time emerged along with the singularity (and therefore this universe).
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Cosmologist and science communicator Sean M. Carroll explains two competing types of explanations for the origins of the singularity. One cosmogonical view sees time as fundamental and even eternal: The universe could have contained the singularity because the universe evolved or changed from a prior state (the prior state was "empty space", or maybe a state that could not be called "space" at all). The other view, held by proponents like Stephen Hawking, says that there was no change through time because "time" itself emerged along with this universe (in other words, there can be no "prior" to the universe).[5] Thus, it remains unclear what combination of "stuff", space, or time emerged with the singularity and this universe.[5]
One problem in cosmogony is that there is currently no theoretical model that explains the earliest moments of the universe's existence (during the Planck time) because of a lack of a testable theory of quantum gravity. Researchers in string theory and its extensions (for example, M theory), and of loop quantum cosmology, have nevertheless proposed solutions of the type just discussed.
Another issue facing the field of particle physics is a need for more expensive and technologically advanced particle accelerators to test proposed theories (for example, that the universe was caused by colliding membranes).
Developing a complete theoretical model has implications in both the philosophy of science and epistemology. For example, it would clarify the meaningful ways in which people can ask the question "why do we exist?".
Cosmogony compared with cosmology
Cosmology is the study of the structure and changes in the present universe, while the scientific field of cosmogony is concerned with the origin of the universe. Observations about our present universe may not only allow predictions to be made about the future, but they also provide clues to events that happened long ago when ... the cosmos began. So the work of cosmologists and cosmogonists overlaps.
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National Aeronautics and Space Administration (NASA)[6]
Cosmogony can be distinguished from cosmology, which studies the universe at large and throughout its existence, and which technically does not inquire directly into the source of its origins. There is some ambiguity between the two terms. For example, the cosmological argument from theology regarding the existence of God is technically an appeal to cosmogonical rather than cosmological ideas. In practice, there is a scientific distinction between cosmological and cosmogonical ideas. Physical cosmology is the science that attempts to explain all observations relevant to the development and characteristics of the universe as a whole. Questions regarding why the universe behaves in such a way have been described by physicists and cosmologists as being extra-scientific (i.e., metaphysical), though speculations are made from a variety of perspectives that include extrapolation of scientific theories to untested regimes (i.e., at Planck scales), and philosophical or religious ideas.
Epistemological limitations to cosmogony
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The assumptions of naturalism that underlie the scientific method have led some scientists - especially observationalists - to question whether the ultimate reason or source for the universe to exist can be answered in a scientific fashion. In particular, the principle of sufficient reason seems to indicate that there should be such an explanation, but whether a satisfactory explanation can be obtained through scientific inquiry is debatable. A scientific examination of cosmogony using existing physical models would face many challenges. For example, equations used to develop models of the origin do not in themselves explain how the conditions of the universe that the equations model came to be in the first place.
Theistic explanations for origins implicate one or more supernatural immortal beings as the first cause, although these are often dismissed as God of the gaps-type fallacies or arguments from ignorance. Such explanations tend to provide no explanation for the existence of the deity, which can be interpreted as simply replacing one existence question with another that a priori cannot be answered. Nondual explanations, by contrast, state that the very question is misleading since it contains erroneous assumptions of beginnings, endings, and the nature of existence itself, and consider the visible universe as phenomenology.
As a result of this, scientific cosmogonies are sometimes supplemented by reference to metaphysical and theistic belief systems. The problem can be summarised as three classical paradoxes. These paradoxes - discussed by both Kierkegaard and Leibniz - are:
- reconciling a doctrine of causation (similar to the 13th century proof of God posed by Thomas Aquinas);
- reconciling the conservation laws ("something from nothing");
- reconciling issues of temporal (as in Zeno's paradoxes) and logical regression.
However, some of the metaphysical principles used to formulate these classical paradoxes no longer enjoy an unchallenged status as laws of thought. For instance, quantum mechanics gives an independent motivation to challenge the principle of sufficient reason.
Theoretical scenarios
Scientists have only early ideas of the young universe (or its beginning, for those who postulate that it had one). As of 2011, no accelerator experiments probe energies of sufficient magnitude to provide any experimental insight into the behavior of matter at the energy levels that prevailed during this period. Therefore, further technological and conceptual advances are needed to test aspects of these theories. Proposed scenarios differ radically, and include String theory and M theory, the Hartle–Hawking initial state, string landscape, brane inflation, and the ekpyrotic universe. Some of these models are mutually compatible, while others are not. The Big Bounce is a theoretical scientific model of the formation of the known universe. It is implied by the cyclic model/oscillatory universe interpretation of the Big Bang, where the "first" cosmological event was the ultimate result of the collapse of a previous universe.[7]
Planck time limitations to cosmogony
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This section may stray from the topic of the article into the topic of another article, Quantum cosmology. Please help improve this section or discuss this issue on the talk page. (September 2011) |
Planck time (10−43 s) is the time it would take a photon traveling at the speed of light in vacua (in a vacuum) to travel a linear distance equal to the Planck length (1.616199×10−35 meters). It has been proposed that this may be the hypothetical "quantum of time" - the smallest measurement of time that has any physically significant meaning.
Although the laws of physics lose (current) experimental support at/before the Planck time, modern science has sought to clarify the nature of these paradoxes - so far with only limited successes. For example, one can apply the current understanding of grand unified theories (GUT's - both quasi-classical, such as general relativity, and modern, such as quantum gravity, superstring, and M-theories) to these three primary cosmogonic paradoxes in thought experiments. While these result in some contradictions and lack completeness in a mathematical sense (being based on axioms that are "merely" self-evident, but not robust under the stresses of radical scepticism), the paradoxes can nonetheless be analysed rationally using the subatomic applications of quantum cosmology - particularly through the employment of the Schrödinger wave equations.
In each case, where general relativity fails as the curvature of space-time invokes singularities from its equations at t = 0, the statistically "gray" nature of quantum cosmology tends to allow a scientific rationale to account for each paradox, and in so doing allows for a scientific perspective on previously theistic terrain. For example, application of quantum "fuzziness" (per the Wheeler–DeWitt application of subatomic position and momentum equations to universal radius and expansion) avoids boundary issues, as developed in the Hartle–Hawking wave function.
All such equations are based on differentials, which assume a continuum, where in our universe, affected by the Planck length and other minimum scales, this continuum has only limited meaning, about which philosophy remains in a state of semantic flux.
See also
- Digital physics
- Ultimate fate of the universe
References
- ^ a b Ridpath, Ian (2012). "A Dictionary of Astronomy". A Dictionary of Astronomy. Oxford University Press.
- ^ a b Woolfson, M.M. (1979). "Cosmogony Today". Quarterly Journal of the Royal Astronomical Society 20 (2): 97–114. Bibcode 1979QJRAS..20...97W.
- ^ Wollack, Edward J. (10 December 2010). "Cosmology: The Study of the Universe". Universe 101: Big Bang Theory. NASA. http://map.gsfc.nasa.gov/universe/. Retrieved 27 April 2011.
- ^ Wollack, Edward J. (10 December 2010). "Cosmology: The Study of the Universe". Universe 101: Big Bang Theory. NASA. http://map.gsfc.nasa.gov/universe/. Retrieved 27 April 2011.
- ^ a b c A Universe from Nothing?, by Sean Carroll, Discover Magazine Blogs, April 28 2012.
- ^ http://genesismission.jpl.nasa.gov/educate/scimodule/Cosmogony/CosmogonyPDF/CosCosmolTT.pdf
- ^ "Penn State Researchers Look Beyond The Birth Of The Universe". Science Daily. May 17, 2006. http://www.sciencedaily.com/releases/2006/05/060515232747.htm. Referring to Ashtekar, Abhay; Pawlowski, Tomasz; Singh, Parmpreet (2006). "Quantum Nature of the Big Bang". Physical Review Letters 96 (14): 141301. arXiv:gr-qc/0602086. Bibcode 2006PhRvL..96n1301A. doi:10.1103/PhysRevLett.96.141301. PMID 16712061.
